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We have a 1968 Cessna 177 Cardinal with a Bush Conversions 180HP Hartzell constant speed prop convertion. A few months ago, we found that the original aft spinner bulkhead from the fixed pitch prop, (which had been modified for the constant speed) had a corner cracked off of it. We determined that the damage was cause by extra stress from a nutplate that was installed too close to one of the obtuse angles on the bulkhead.
We decided to replace the aft bulkhead with one that was designed for a constant speed prop, so the new one wouldn't crack in the same fasion.
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| The First thing we did was compare the old broken bulkhead with the "new to us" replacement. The replacement was off a early model Cessna 182RG. It was designed for a McCauley constant speed prop, which has a rounder shank than the Hartzell which the coversion uses. The reason we choose this one is because the offset from the starter ring gear was correct for the cowl, and 8 out of the ten holes lined up with our notably odd spinner. | |||||||||||||
| To make it work, we needed to remove the before said 'McCauley ears' and drill two new holes to install the last two screws. The first picture is of the new bulkhead dry fitted into the cowl with the old bulkhead held up to it to make sure the holes lined up. | |||||||||||||
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| What we did next was install the spinner on the new bulkhead and drill the two holes that didn't line up. Then install a nutplate backwards and use that as the template to drill and countersink the hole for the rivet. | |||||||||||||
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| The next step is to line the nutplate on the correct side of the bulkhead and use the screw to pull it tight against the bulkhead.
Then find the correct length rivet either by experience or by a formula of material thickness+1.5 times the rivet diameter. In this case the rivet is a 3/32's. Then put the rivet in and use a rivet squeezer to install it tightly. |
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| For the last major mod we drilled out the rivets for the ears and removed them entirely. The reason to do this last is in case the new holes didn't work, the bulkhead would still be good for it's original application. We then painted it and and installed in on the aircraft. We then marked the area where the prop blades would rotate to when in high pitch with a Sharpie® to make sure they weren't touching the new bulkhead when the prop was cycled.
We got an excellent deal on this bulkhead at $150. I highly recommend Aero Propellor in Hemet CA. for parts and overhauls. They recently burned to the ground but should be up and running in a few months. Overall this took us one afternoon of two people working. |
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| 2003 Copyright Stephen Samuelian | |||||||||||||